Abou the slowdown, I'm pretty sure you are not using WhateverGreen.kext, right? Try installing it. If you already have, run kextstat to see if is loaded.
You can order a DW1560, It's works very nice and have Continuity, AirDrop and Handoff. Only Instant Hotpot that sometimes don't work.
Send me the logs about the panics

- Laggy touchpad: You're right, I still have original (my T460 has not arrived yet) and I can confirm. Had not realized yet why use with keyboard and mouse connected on a second monitor at work.
- System slowing down: You sure the Speed Step is working? Why usb dongle? Why do not you replace a wireless card?
- Sometimes it boots at 3rd attempt: Do this, see at boot what's happening next. But if it's kernel panic it will not appear in the log, right?

After I talked to you, I did some testing with AppleALC and VoodooHDA:
AppleALC 1.34
- Internal Speaks ok.
- No headphones (internal speaks stops but no sound on headphones).
- Still working after sleep.
- Tried all codecs from ALC292 per Wiki (12, 18 and 28)
VoodooHDA 2.9.1 V12
- Internal Spekas ok, but more low than AppleALC (tried VoodooHDAEnableHalfVolumeFix = <true/>, but no success)
- Headphones ok
- Still working after sleep!
- CodecCommander.kext not needed
For me, the best option wihin now is VoodooHDA.
Make try: https://sourceforge.net/projects/voodoohda/
Remove AppleALC.kext and put VoodooHDA.kext and "kextcache -i /"

@tluck Fixed your BIOS signature:
https://www.sendspace.com/file/w9cafl
I could not understand how you are flashing your BIOS, this file was inside the folder: 83ET76WW/
[EDIT]
Two volumes on BIOS has been fixed:

With the wireless whitelist removal some AMT features are also disabled with the mod and on some Lenovo you get 5 beeps (twice) on boot.
This is because of RSA signature that as verified on boot. I can fix that.
If anyone want, send me the DUMP of the current patched BIOS.
Soon I will make a guide so you can do it alone.
[EDIT]